(19)
(11) EP 0 391 571 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
08.07.1992 Bulletin 1992/28

(43) Date of publication A2:
10.10.1990 Bulletin 1990/41

(21) Application number: 90302999.9

(22) Date of filing: 20.03.1990
(51) International Patent Classification (IPC)5: H04L 25/08, H03K 19/018, H03K 17/16
(84) Designated Contracting States:
DE FR GB

(30) Priority: 07.04.1989 US 335010

(71) Applicant: Hewlett-Packard Company
Palo Alto, California 94304 (US)

(72) Inventor:
  • Wheeler, Richard L.
    San Jose, California 95129 (US)

(74) Representative: Colgan, Stephen James et al
CARPMAELS & RANSFORD 43 Bloomsbury Square
London WC1A 2RA
London WC1A 2RA (GB)


(56) References cited: : 
   
       


    (54) Driver-receiver pair for low noise digital signaling


    (57) A digital signalling circuit employs a spaced apart driver and receiver pair in which the signal current originates at the receiver and is constant in time. The receiver chip includes a constant current source connected to the power supply plane and one termination of a signal line, a termination resistor connected across the signal line termination to the ground plane, and a sense amplifier connected to the signal line termination for sensing the voltage level or the signal line. The driver chip comprises a single switching transistor connected across the opposite end of the signal line to the ground plane, and is not directly coupled to the power supply plane. When the driver switching transistor is on, the signal line is grounded and the termination resistor in the receiver is effectively shorted out. When the driver switching transistor is turned off, the signal source current at the receiver charges up the signal line and develops a voltage across the termination resistor. Since a constant current source is used, any inductance in the circuit has no effect on the power supply voltage. Power supply bypass capacitors are effectively removed from the circuit reducing signal propagation times.







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